This is the first stage of a multivariate young adult follow-up study of a core sample of 124 boys with the hyperkinetic/minimal brain dysfunction (HK/MBD) syndrome and their 68 full brothers, plus a replication sample of 64 comparable boys with the HK/MBD syndrome and their 42 full brothers. The core and replication patient samples were originally seen as referrals to the University of Iowa Child Psychiatry Outpatient Service between 1967 and 1972. The core sample was followed up five years after referral as young adolescents. Data from the referral period and from the adolescent follow-up are now stored on tape as easily-accessible computer archives. In this initial stage, 59% of the 298 subjects are being seen within two years after their 21st birthday and administered a multitrait-multimethod battery of cognitive, achievement, behavioral, personality, and psychiatric tests, interviews, and ratings. Results of planned multivariate analyses will ultimately provide a systematic description of HK/MBD boys as young adults, with sibling controls and cross-validation. Data will also be available to identify and to replicate, by means of multiple regression techniques, those background, referral, and treatment variables that predict young adult status.